In recent years, a sensor node including in its inside a temperature sensor, a moisture sensor, or a human sensor configured to detect the presence of a human is often installed in a house or an office. Such a sensor node is essential for achieving a more comfortable life environment. The sensor nodes distributed and disposed in a house or the like can transmit and receive data with a host device for the sensor nodes by wireless communication. The host device performs unified management of environmental information on the house or the like, and uses the environmental information for control of lighting, air conditioning, and the like. Alternatively, it is also possible to construct a security system when the sensor node including the human sensor is used.
Each sensor node is not necessarily disposed in a location in the vicinity of an electrical outlet. Thus, a direct current power source such as a battery or a button battery is often used as a power source. Further, since the sensor node is installed in order to obtain the environmental information on the house or the like, the sensor node repeats an operation of transmitting data on temperature, moisture, or the like to the host device at a constant cycle. Further, since the sensor node is not disposed for a purpose such as interior decoration, and is often installed in an out-of-sight place. For that reason, a large amount of cost (maintenance cost) is needed to replace the battery of the sensor node. Thus, a sensor node that does need battery replacement as little as possible is demanded. That is, a sensor node, in which the service life of the battery is increased, is demanded. More specifically, the service life of the battery in units of year is desired in order to reduce the maintenance cost for charging or replacement of the battery.
Then, various technologies for reducing power consumption of the sensor node are present. To take an example, in a period except when the sensor mode is operated to obtain and transmit the environmental information, transition to a sleep mode is made. In the sleep mode, only a minimum function is activated, and the other functions are stopped.
Patent Literatures (PTLs) 1 and 2 each discloses a technology for suppressing a peak of a current to be consumed by a wireless communication device by operating modules included in the wireless communication device in a predetermined order.
Patent Literature 3 discloses a power supply device in which a battery and a capacitor are disposed in parallel to suppress a peak of a current to be supplied to a load.
[PTL 1]
JP Patent Kokai Publication No. JP2007-243933A
[PTL 2]
JP Patent Kokai Publication No. JP2007-079669A
[PTL 3]
JP Patent Kohyo Publication No. JP2008-529177A